Human reproduction is controlled by the pulsatile secretion of the hypothalamic neuropeptide, Gonadotropin-releasing hormone (GnRH), from a network of GnRH neurons. Failure of GnRH neuronal development or its secretion/action results in a rare human genetic disease called isolated GnRH deficiency (IGD). Kallmann Syndrome (KS) represents a distinct neurodevelopmental form of IGD which is characteristically associated with anosmia. To-date, only ~30% of genes linked to KS are currently known. Mutations in two axonal guidance genes, KAL1 and NELF were the first KS-associated genes to be discovered. However, until recently, no similar axonal guidance genes have been implicated in KS. The genetic, molecular and phenotypic characterization of three novel axonal guidance genes forms the basis of this proposal. Five unrelated patients fitting the diagnosis of Moebius syndrome, a complex neurodevelopmental syndrome, were recently found to harbor a de novo heterozygous missense mutation (p.E410K) affecting the TUBB3 gene, which encodes for an axonal guidance molecule called neuronal ?-tubulin isotype 3. The PI has now identified that all these patients also display KS, suggesting TUBB3 as a novel KS gene. In addition, mutations in SEMA3A, another axonal guidance molecule and mutations in SOX10, a neural crest migratory gene, were also recently implicated as cause of KS. In Specific Aim #1, the PI will assess the role of these three novel neuro-developmental genes involved in axonal guidance (TUBB3, SEMA3A, and SOX10) in the pathogenesis of IGD by studying the prevalence of mutations, their molecular causal mechanisms and their genetic interactions with other IGD genes. In Specific Aim #2, the reproductive and non-reproductive phenotypes of patients harboring mutations in these three genes will be examined to define their biological role in GnRH neuronal ontogeny and in other organ systems. KS has been thought to represent an aberrant axonal guidance disorder in humans and this proposal will provide confirmatory evidence to this hypothesis. The long term goal of the PI is to become an independently funded clinical investigator and develop a comprehensive research program to study disorders of human reproduction. To achieve his career goals, the PI has assembled a highly dynamic mentoring team to oversee his proposed research. In addition, he has identified key training objectives that will be achieved through practical research experience, coursework and didactic learning. This rigorous career development and research training plan will help him to build on his existing research strengths, acquire new clinical investigatory skills and facilitate his transition to independence.